1. Field of the Invention
The present invention relates generally to railroad crossings having precast concrete panels and methods for making such crossings and more particularly to such crossings which include ties that support both railroad tracks and the panels.
2. Description of the Related Art
When a roadway crosses railroad tracks, a crossing must be constructed to permit traffic to pass over the tracks as smoothly as possible. Typically the top surfaces of each of the tracks are in substantially the same plane as the roadway on either side of the tracks. The crossing comprises material which is placed on either side and between the tracks to present a surface generally planar with the surface of the roadway and the top surfaces of the tracks.
Timber, asphalt, poured concrete and precast concrete are examples of prior-art materials which have been used to construct railroad crossings.
Two types of prior art precast concrete crossings include: (a) precast structures which are received under the railroad track in the crossing and which substitute for the railroad ties that support the track on either side of the crossing; and (b) precast structures which are supported on ties in the crossing adjacent railroad track which is also supported on the ties.
One example of the latter type of precast concrete crossing is disclosed in U.S. Pat. No. 5,181,657 to Davis for a composite rubber/concrete railroad grade crossing system. In Davis, substantially rectangular precast panels have a metal corner portion, made of angle iron, cast into the panel around the upper perimeter thereof. Elastomeric pad units abut either side of each rail with a plurality of central precast concrete panels laid end to end in the center and narrower precast concrete panels laid end to end on the outer sides of each track. The panels thus hold the elastomeric portion in place and are in turn restrained from longitudinal movement along the tracks by brackets which are bolted to the ties and which abut the panels at each end of the crossing.
The metal corner portions are provided to prevent the concrete corners from crumbling as a result of traffic passing thereover. In some prior art installations using similar panels, the metal corner portions on adjacent panels are welded together to prevent independent movement of separate panels.
Precast panels for use in grade crossings such as those shown in the Davis patent are created using a generally rectangular mold. A rectangular angle iron frame is placed on an upper portion of the mold. Thereafter concrete is placed in the mold to the level of the top surface of the frame thereby casting the metal frame into the upper surface of the panel.
Problems exist with using panels having metal corner portions such as those disclosed in the Davis Patent. Whether welded together or not, the metal creates a conductor capable of shunting currents between the rails which can create signalization malfunctions. Such prior art panels include opposing metal corner portions which are each within a few inches of an adjacent rail. In the presence of salt and water, especially in freezing temperatures, a conductive path between the rails is easily set up whether or not the corner portions are welded to one another.
The welds are also problematic when maintenance is required on the railroad bed in the crossing. This requires that the panels be removed, which in turn requires breaking the welds on any of the panels that are welded together. After maintenance of the bed, the panels are returned to the crossing and rewelded.
In some prior art crossings, panels like those shown in the Davis patent were both welded together and screwed, via bores through the panels, to wood ties which support the panels. This further restrained panel movement but did not alleviate problems caused by the metal corner portions. In addition, screwing into the wooden ties deteriorates them.
It would be desirable to provide a precast concrete panel for use in a grade crossing on a roadway which overcomes problems associated with prior art panels.
It would also be desirable to provide such a panel which is highly resistant to deterioration caused by freezing.
It would also be desirable to provide such a panel that will withstand heavy vehicle and rail traffic.
It would also be desirable to provide such a panel which reduces signalization problems.
It would also be desirable to provide such a panel with increased durability.
It would also be desirable to provide such a panel which overcomes problems associated with using metal corner portions as in the prior art panels.
It would also be desirable to provide such a panel which could be secured in position without welding the panels to one another or screwing the panels to the railroad ties supporting the track.
It would also be desirable to provide such a panel which can be easily removed and replaced for maintenance to the rail bed beneath the crossing.
It would also be desirable to provide a method for making such a panel.